1. Field of the Invention
The present invention relates to a position sensing device which senses the position at which a moving object is stopped (hereinafter referred to as stopped position).
2. Description of the Related Art
Recently, especially with regard to compact cameras, many cameras equipped with a power zoom lens have been developed. When a zoom lens is utilized, usually the aperture opening value is changed in accordance with a focal length of the lens, and accordingly, the aperture opening value must be input to the camera control means to carry out automatic exposure control with a zoom lens. Further, in a camera in which an exposure program, for example, is changed in accordance with focal length, data regarding of the focal length of the lens must be input to the camera control means.
Therefore, in a conventional device, a position of a zoom ring, which causes a variable magnification lens groups the variator lens and a compensator lens) to move relatively close to and apart from each other, is sensed and optical data such as corresponding aperture opening value and focal length of the lens is obtained from the lens position data.
Two methods of sensing the stopped position of the zoom ring are known; one in which a range of movement of the zoom ring is divided into a plurality of sections, each section is given a different code, and the codes are discriminated by a code discrimating mechanism, and another in which periodically varied codes are given to the entire range of movement of the zoom ring and a code change counting mechanism is used to count the number of changes of the codes from a base position thereof.
In the position sensing mechanisms described above, however, if a sensing part of the discrimating mechanism such as brush or beam for sensing the stopped position stops on a boundary between two codes, reading errors may occur.